Post-translational glycoprotein modifications regulate colon cancer stem cells and colon adenoma progression in Apc(min/+) mice through altered Wnt receptor signaling

Deletion of GnT-V (MGAT5), which synthesizes N-glycans with β(1,6)-branched glycans, reduced the compartment of cancer stem cells (CSC) in the her-2 mouse model of breast cancer, leading to delay of tumor onset. Because GnT-V levels are also commonly up-regulated in colon cancer, we investigated their regulation of colon CSC and adenoma development. Anchorage-independent cell growth and tumor formation induced by injection of colon tumor cells into NOD/SCID mice were positively associated with GnT-V levels, indicating regulation of proliferation and tumorigenicity. Using Apc(min/+) mice with different GnT-V backgrounds, knock-out of GnT-V had no significant effect on the number of adenoma/mouse, but adenoma size was significantly reduced and accompanied increased survival of Apc(min/+) mice with GnT-V deletion (p < 0.01), suggesting an inhibition in the progression of colon adenoma caused by deletion of GnT-V. Decreased expression levels of GnT-V down-regulated the population of colon (intestine) CSC, affecting their ability for self-renewal and tumorigenicity in NOD/SCID mice. Furthermore, altered nuclear translocation of β-catenin and expression of Wnt target genes were positively associated with expression levels of GnT-V, indicating the regulation of canonical Wnt/β-catenin signaling. By overexpressing the Wnt receptor, FZD-7, in colon cancer cells, we found that FZD-7 receptors expressed N-linked β(1,6) branching, indicating that FZD-7 can be modified by GnT-V. The aberrant Wnt signaling observed after modulating GnT-V levels is likely to result from altered N-linked β(1,6) branching on FZD-7, thereby affecting Wnt signaling, the compartment of CSC, and tumor progression.